Oracle: Get UNIX epoch

SELECT
  ROUND((SYSDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60) AS EPOCH
FROM DUAL;

The subtraction tells how many days is the difference, as a floating point number. Multiply it with 24 hours * 60 minutes * 60 seconds to scale it to seconds. Round it as we don't want sub-second precision.

If the time zones don't match up, use UTC:

SELECT
  ROUND((CAST(SYS_EXTRACT_UTC(SYSTIMESTAMP) AS DATE) - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60) AS EPOCH
FROM DUAL;